幾丁聚醣丙酸水溶液之光散射研究

Light Scattering Study of Chitosan in Propionic Acid Aqueous Solutions

郭豪飛(Hou-Fei Guo)

指導教授 ： 余子隆 ； 林秀麗

元智大學/工程學院/化學工程與材料科學學系/碩士(2001年)

摘要

本論文乃研究水溶性聚電解質—幾丁聚醣(chitosan)於不同pH值之丙酸水溶液中分子形態的變化。幾丁聚醣在有機酸水溶液下帶有-NH3+的正電荷，在不同pH值的丙酸水溶液中，幾丁聚醣的正電荷含量不同，所產生的電荷相斥作用會因pH值不同而改變，使得幾丁聚醣隨著pH值變化而有不同的分子形態。使用靜態光散射可以量測出分子環動半徑Rg(radius of gyration)、第二維里係數A2(second virial coefficient)和分子量(weight average molecular weight)，而歸納出幾丁聚醣分子形態和pH值之間的關聯性。使用動態光散射可求得聚合體在稀釋溶液中的傳動滲透係數Dt(translational diffiusion coefficient)進而計算其水動半徑Rh(hydrodynamic radius)分佈。實驗結果顯示，極限黏度[η]、第二維里係數(A2)、環動半徑(Rg)及水動半徑(Rh)、r(Rg/Rh)值皆隨溶劑pH值下降而增大，但分形維數隨pH值下降而下降，顯示分子形態隨著pH值下降越趨向於桿狀結構。pH值增加則幾丁聚醣分子因帶正電荷密度減少，分子內電荷排斥力下降而趨向於coil形態。我們亦取本實驗室前畢業生柏榮生論文，幾丁聚醣在乙酸水溶液之數據與本報告數據作比較。我們發現在相同pH值下，幾丁聚醣在丙酸水溶液中有較大的粒徑，分子鏈較容易伸展開。

關鍵字

幾丁聚醣 ； 極限黏度 ； 靜態光散射 ； 動態光散射 ； 分形維數

並列摘要

In this study,we inverstigated the chain conformation of chitosan in propionic aqueous solutions at various pH values. The intrinsic viscosity [η] were measured using Ubbelohde viscometer. The second virial coefficient (A2), radius of gyration , and weight average molecular weight (Mw) can be obtained from static light scattering and hydrodynamic radius from dynamic light scattering. The experiments results revealed that [η], (A2), and decreased with increasing pH value. Increasing [H+] concentration resulted in an increase in the positive charge [-NH3+] group of chitosan. The charge repulsion of chitosan leads to increases both in molecular size and solubility of chitosan in water as pH decreases. The study of fractal dimesion also revealed that the molecular chain dimesion becomes more compact as pH increased. We also compared experimental data of chitosan in acetic aqueous solution with those in propionic aqueous solution. In the same pH value, we found that molecular size of chitosan in propionic aqueous solution was larger than that in acetic aqueous solution.

並列關鍵字

chitosan ； intrinsic viscosity ； static light scattering ； dynamic light scattering ； fractal dimesion

參考文獻

Amal R., Raper J. A., and Waite T. D. J. Colloid Interface Science., 140(1), 158-168 (1990)。

Anthonsen M. W., Varum Kjell M., and Smidsrod, O.,”Solution properties of chitosans:conformation and chain stiffness of chitosans with defferent degrees of N-acetylation,”Carbohydrate Polym.,22,193-201 (1993)。

Austin P. R., Brine C. J., Castle J. E., and Eikaksi J. P., “Chitin”, New Facets of Research Science., 212, 749 (1981)。

Borodinsky L., and King R. B., “Poly(vinyliminomethylenes)” , Maromol., 18(11), 2117-2120 (1985)。

Chen R.H., Lin J.H. and Yang M.H., “Relationship between the chain flexibilities of chitosan molecules and physical properties of their casted films”, Carbohydrate Polymers , 24,41(1994).